Check out our additional resources:
By Walt Boyes, Editor in Chief
Wireless systems are coming to your plant. Fact is, this is old news. Weve talked about it for a while now. ( See our Field Guide to Industrial Wireless).
You probably already have wireless devices in your plant, because wireless isnt limited to sensor networks. You already have analog wirelesshandi-talkies, maybe some point-to-point analog wireless sensor signals, 802.11 a/b/g/n WiFi, cellphones and maybe even some Bluetooth M2M (machine to machine) connections. You may even have one of the newer digital mesh-based wireless sensor networks.
You may have more than one.
The problem now is how to establish policies, procedures and engineering best practices for using wireless systems effectively. This is because there are three completely incompatible, non-interoperable, and potentially interfering standards in the traditional field device space. These are WirelessHART, ISA100.11a and ZigBee PRO.
Hoarding Their Moldy Peanuts
The ISA100 standards committee, which was formed to help industrial wireless users, especially those in the process industries, has been deadlocked in a struggle for the control of the ISA100.11a standard (see editorial Not Playin Nice) for three years. One faction wants the adoption of the existing WirelessHART standard (HART 7.1), while another faction wants adoption of a standard that is very close to the Honeywell OneWireless proprietary implementation. These two factions have been in a close-in knife fight for years, with no end in sight. A group of end users on the committee have proposed of the adoption of another standard, ISA100.12, which would be the WirelessHART standard. At this writing, it isnt clear what that will do, other than put two mutually incompatible and non-interoperable standards under the ISA100 umbrella. Another group of ISA100 members has acted to try to do the same for ZigBee PRO, which might wind up as ISA100.13.
Until the standards committee gets off its collective posterior and works something out about interoperability and incompatibility (see sidebar for definitions), it is going to be up to end users to set evaluation criteria and policies and procedures and generate engineering best practices.
What should those criteria and best practices be? One of the anonymous end users who responded to this years Control/ISA100 Wireless Survey put it very bluntly:
ISA and my wireless vendor need to specify what plant wireless surveys I must conduct prior to designing my new wireless network. They must tell me how to do it and provide the tools, or they need to do it for me. They need to develop engineering guidelines so I know how to mount my field instruments and field routers to get a reliable wireless network. ISA needs to develop wireless documentation requirements, such as symbology for P&IDs, network diagrams, ISS sheets, tag naming and others, so I can document my system adequately. When I spec and purchase my instruments, I need to know what factory configuration is required to make sure they will plug in and play when turned on. I dont want to be forced into site configuration. My vendor needs to tell me how to configure wireless devices in my off-line project DCS database, including use on displays, engineering config, use in logic, etc. And finally, I need to understand what are the appropriate SAT & FAT tests required for wireless devices, if any.
It would be nice, of course, if ISA100 would generate this information, but it doesnt seem like thats on the horizon any time soon, although there is a team working on it.
Meanwhile, the benefits of wireless in your plant are still greater than the additional pain and effort you will have to go through to manage three completely incompatible standards.
Interestingly, the three standards, WirelessHART, ZigBee PRO, and ISA100.11a all use the same radio and all are mesh networks. What this means is that it is probably practical to have more than one of them in your plant. A pain, to be sure, but practical.
Why is it going to be practical? It will be possible to use multiple IEEE802.15.4 networks in the same air space because they can be made to not interfere with each other by means of channel-hopping, channel-blanking and other firmware capabilities. This does not mean they will interoperate, and they wont be interchangeable, and theres the pain.
The ISA100 committee expects to release an ISA100.11a standard late this year or early next year. Honeywells global director of wireless, Jeff Becker, announced at the 2008 Honeywell User Group Americas, Our implementation of Honeywell OneWireless is going to be convertible by a firmware upgrade to the final ISA100.11a standard.